High Fidelity Stereo Pre-Amplifier

Mullard Wireless, London (see also Mullard Radio Valve)

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  • Year
  • 1960
  • Category
  • Kit (Parts plus instruction) or building instructions only
  • Radiomuseum.org ID
  • 367511

Click on the schematic thumbnail to request the schematic as a free document.

 Technical Specifications

  • Number of Tubes
  • 4
  • Main principle
  • Audio-Amplification
  • Wave bands
  • - without
  • Power type and voltage
  • Powered by external power supply or a main unit.
  • Loudspeaker
  • - For headphones or amp.
  • Material
  • Metal case, TUBES VISIBLE
  • from Radiomuseum.org
  • Model: High Fidelity Stereo Pre-Amplifier - Mullard Wireless, London see
  • Shape
  • Chassis only or for «building in»
  • Notes

  • Design‑only stereophonic pre‑amplifier published by Mullard in Circuits for Audio Amplifiers, 1960. Intended for home construction and for use with the Mullard 20W, 10W and 3W power‑amplifier circuits. Provides RIAA and 78 rpm disc equalisation, tape replay equalisation for high‑impedance heads, radio and auxiliary inputs, passive tone controls and a low‑impedance monitoring output. Uses two EF86 pentodes per channel with frequency‑selective feedback in the first stage.

    Technical Data

    • Valves: 4 × EF86 (two per channel)
    • Topology: Two‑stage pentode pre‑amplifier per channel
    • Equalisation:
      • RIAA microgroove
      • 78 rpm
      • Tape replay (CCIR above 100 Hz, modified below 100 Hz)
      • Radio (flat response)
      • Auxiliary (same as radio input)
    • Tone Controls: Passive bass and treble, wide‑range boost/cut
    • Balance Control: Log/antilog ganged pair between stages
    • Volume Control: Dual‑ganged potentiometer after tone network
    • Stereo Switching: Normal, reversed, dual‑channel mono
    • Auxiliary Output: ~250 mV, low impedance, taken from second EF86 anode load
    • Input Sensitivities:
      • Magnetic (microgroove): 5 mV
      • Magnetic (78 rpm): 15 mV
      • Crystal (microgroove): 70 mV
      • Crystal (78 rpm): 210 mV
      • Tape replay: 4 mV at 5 kHz
      • Radio/Aux: 330 mV
    • Input Impedances:
      • Magnetic: ~100 kΩ
      • Crystal: 100 kΩ
      • Tape: ~80 kΩ
      • Radio/Aux: 1 MΩ
    • Output Level: Sufficient to drive Mullard 20W amplifier; optional attenuator for 10W or 3W amplifiers
    • Distortion: <0.15% at normal output; 0.24% at ×10 output
    • Power Requirements:
      • HT: 230 V at 3 mA per channel
      • LT: 6.3 V at 0.4 A per channel
  • Mentioned in
  • - - Manufacturers Literature (Circuits for Audio Amplifiers, 2nd Edition, 1960. P.127-130)
  Mullard Circuits for Audio Amplifiers, 2nd Edition, 1960. P.127-130 2347 KB
  • Documents regarding this model
  • Author
  • Model page created by Gary Cowans. See "Data change" for further contributors.

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